1. Field of the Invention
The present invention relates to a connection circuit of an interconnect device, and more particularly, to a connection circuit capable of detecting erroneous wiring in an interconnect device.
2. Description of the Related Art
In some cases, a peripheral device is connected to an interface for connecting the peripheral device when a machining tool is used. FIG. 4 is a diagram illustrating a connection circuit of an interconnect device of the related art. A plurality of I/O units 140 are connected to a power unit 110 through a power line 220, and a safety fuse 120 is connected between the power unit 110 and each I/O unit 140. In addition, each I/O unit 140 is grounded through a ground line 250.
In wiring having such a configuration, when an operator connects the I/O unit 140 of the peripheral device, in some cases, the power line 220 and the ground line 250 may be short-circuited due to erroneous wiring, a defect in a connection cable, or the like. If a power-on signal 200 is input to the power unit 110 in this state, the safety fuse 120 may be melted due to the short-circuit state.
In this case, if it is obvious that the power line 220 and the ground line 250 are short-circuited, the short-circuit state can be addressed. However, if the short-circuit state is unknown, an operator may think it as an erroneous operation of a machine, and turn on the power again or change the wiring and then turn on the power again. In this case, since the power is turned on again while an actual short circuit state is not addressed, the safety fuse 120 may be melted again.
Japanese Patent Application Laid-Open No. 2003-189467 discloses a technique of using a poly-switch which is an element having an increasing resistance when an overcurrent flows instead of the safety fuse in order to prevent the safety fuse from being repeatedly replaced in the event of a wiring error (see FIG. 5). The poly-switch cuts off the current using heat generated in the event of an overcurrent. However, its temperature decreases to a predetermined level, so that the connection state is recovered. For this reason, it is not necessary to replace the safety fuse even when an overcurrent occurs.
In the example of FIG. 4, since the safety fuse is inserted into the wiring, the safety fuse is melted when an overcurrent occurs. In order to prevent such a disadvantage, the power may be turned on by checking the wiring again using a conduction tester before the power-on operation. However, in this method, it is required to separately prepare the conduction tester and individually check the wires one by one using the conduction tester. This is a cumbersome work.
In the technique discussed in Japanese Patent Application Laid-Open No. 2003-189467, replacement of the safety fuse caused by the melting in the event of an overcurrent is not necessary because the poly-switch is employed. However, the poly-switch is an element for a low current of milliamperes. Therefore, compared to the safety fuse, a cut-off time is necessary when the poly-switch is employed in a circuit having a normal current of several amperes. In this case, it may be difficult to protect the circuit from the overcurrent.